Qualitative and quantitative self-tests have developed gradually over the last half century. Since the first self-test for glucose, introduced 50 years ago, advances in dry reagent chemistry and the technology associated with device design have lead to self-test kits capable of performing complex quantitative analysis from finger stick whole-blood samples by an untrained person. The evolution of self-tests from the initial glucose test of 1941 to the current state-of-the-art non-instrumented whole-blood quantitative cholesterol test (Allen et al, Clin. Chem. 36:1591-1597 (1990)) was directed by a number of factors, including the need for testing by consumers in the privacy of their homes.
The first device, called the CLINITEST.RTM. for measurement of glucose, was developed by the Ames division of Miles Laboratories and used a dry formulated effervescent tablet that was added to a solution of diluted urine (Free et al, Lab. Med. 15:595-601 (1984), Compton and Treneer U.S. Pat. No. 2,387,244 (1945)). The reaction of glucose in the sample with copper sulfate in the tablet produced a color change as a result of a redox reaction, which was then compared to a color block chart to estimate the amount of glucose in the sample. The positive effect of the CLINITEST.RTM. on the treatment of diabetes was very real and established for the first time the contribution of convenience in allowing analytical chemistry to be used by the non-technical person.
The above test was then followed in the 1950s by the development of solid-phase dipstick tests for the measurement of glucose and proteins, among others, in urine (Free et al, Clin. Chem. 3:163-168 (1957); Comer, Anal. Chem. 28:1748 (1956); Free et al, Gastroenterology 24:414-421 (1953)); and later in the 1960s and 1970s their measurement in whole-blood samples (Free et al, Lab. Med. 15:595-601 (1984); Free et al, Clin. Chem. 30:829-838 (1984); Balazas et al, Lanset 1:1232 (1970); Kallner, Clin. Chem. 3:1-16A (1983). These tests basically involve reaction of the analyte in a sample with reagents on the dipstick pad, resulting in formation of colored product(s). Nature and intensity of color gives the measure of analyte in the sample. For whole blood samples, the red cells are first separated prior to the reaction of plasma with the reagent on the pad. These tests are read visually and provide at best, semi-quantitative results. Availability of portable instruments in the 1970s and 1980s have allowed these dipstick tests to provide quantitative results (Balazas et al, Lanset 1:1232 (1970); Free, A. H. Pure Appl. Chem. 54:2063-2073 (1982). Because of the cost associated with instruments, these quantitative tests have mostly found use in professional markets. Perhaps the most important single exception is the whole-blood quantitative glucose tests for use in the home market. Diabetic patients must monitor their glucose level more than once a day for effective management of the disease with insulin, justifying the cost of the needed instrument.
The next major advancement in non-instrumented tests came with the application of immunochemical reagents on a solid support. This led to a number of commercially useful diagnostic tests including those for HCG (pregnancy), LH, FSH, CKMB, Staphylococcus, and rubella. Measurement of the hormone HCG to detect pregnancy was among the first of these tests to become commercially successful in the home market. The first home pregnancy test, the E.P.T..TM. used a solution phase chemical reaction that formed a brown ring on the surface of the urine solution in the presence of HCG. The 2 hour long protocol associated with this test was sensitive to vibration and timing, causing false results. These disadvantages were eliminated during the next decade of evolution, which saw the development of modern solid-state devices.
In the late 1980s, a completely self-contained pregnancy test was introduced by Unipath Ltd. and marketed by Whitehall Laboratories. This test, called the CLEAR BLUE EASY.TM., had all the reagents dry formulated along a laminated membrane, used conjugated colored latex micro-beads as the signal reagent, and used a capillary migration immunoconcentration format. This test is complete in 3 minutes and is the first one-step assay of its kind.
Two additional test systems that appeared in the late 1980s were the LIPOSCAN.TM. by Home Diagnostics Inc. and the CHEMCARD.TM. by Chematics Inc. Both tests measure cholesterol in whole-blood using visual color comparison. Since visual color matching is subjective, these tests do not achieve the quantitative performance necessary for cholesterol testing (Pradella, M., et al Clin. Chem. 36:1994-1995 (1990).
For many analytes such as the markers for pregnancy and ovulation, qualitative or semiquantitative tests are appropriate. There are, however, a variety of analytes that require accurate quantitation. These include glucose, cholesterol, HDL cholesterol, triglyceride, a variety of therapeutic drugs such as theophylline, vitamin levels, and other health indicators. Generally their quantitation has been achieved through the use of an instrument. Although suitable for clinical analysis, these methods are generally desirable for point-of-care testing in physicians offices rather than in the home due to the expense of the instrument.
Recently, a number of non-instrumented methods for accurate measurement of analytes have started to emerge. The key to achieving instrument-free quantitation is through the use of migration distance rather than color matching as the visual signal. In migration distance assays, chemical/biochemical reactions occur as the analyte is wicked through a solid support. During wicking the analyte reacts with a signal-producing reagent and forms a visible signal along the support. The migration distance or the distance of signal border is related to analyte concentration. The operator reads the height of the color bar, much the same way one reads a thermometer, and finds the concentration from a calibrated scale.
There are only a handful of migration-type assays commercially available. These include the ENVIRONMENTAL TEST SYSTEMS QUANTAB.TM., which measures chloride in swimming pools and during the mixing of concrete; Syva's ACCULEVEL.RTM. for the measurement of therapeutic drugs; and ChemTrak's ACCUMETER.RTM. for measurement of cholesterol in whole-blood. Other companies such as Enzymatics and Crystal Diagnostics have more recently announced the introduction of their Q.E.D..TM. and CLINIMETER.TM. technologies to measure alcohol in saliva and cholesterol in blood. ActiMed Laboratories describes the newest thermometer-type assay device (Ertinghausen, G., U.S. Pat. No. 5,087,556 1992).
These single use thermometer-type non-instrumented devices (for quantitation) and the non-instrumented color comparison devices for qualitative measurement represent the state-of-the-art at this time. Although these devices have shown adequate performance, they have several problems associated with reliability and convenience. First and foremost, the colors generated on these devices are not always uniform and sharp. In the case of the migration type assays the border is often light in color, unclear and difficult to read. This translates directly to user errors since the user must make a judgment related to the position of the color band border. In the case of the non-instrumented pregnancy tests it is sometimes difficult to visually interpret the intensity of the colored spot (especially at HCG concentrations close to the cut-off sensitivity) and result interpretation is sometimes a problem. Any time a non-technical operator is required to make a visual judgment or interpretation, an error is possible and sometimes unavoidable. Second, the assay protocol for these tests is sometimes difficult and lengthy taking 15 minutes to 1 hour to obtain a result. Third, these tests often do not have sufficient procedural and reagent controls to assure adequate test performance. Fourth, non-instrumented devices can only measure endpoint type tests (enzyme rate cannot be measured), and therefore, the potential analyte menu is limited.
A recent article in Clinical Chemistry (Daviaud, et al, Clin. Chem. 39:53-59 (1993)) evaluated all 27 home use pregnancy tests sold in France. The authors state, "among the 478 positive urine samples distributed, 230 were falsely interpreted as negative. The main explanation for such a high percentage of false negative results was difficulty in understanding the explanatory leaflets accompanying the kits and hence in reading the results". Clearly there is room for improvement in what is currently state-of-the-art.
The device of this invention is a disposable, single use electronic instrument that is entirely self-contained, including all chemistry reagents. The user simply adds a body fluid sample, and minutes later a numerical digital result appears on the display. The device provides procedure and reagent check systems that permit the device to achieve a high level of reliability. The numerical display overcomes the most significant problem associated with non-instrumented devices. The subject invention marks a significant step in the evolution of self-tests.
Small instruments, some pocket-sized, which measure glucose or other analytes are commercially available and common in use. Examples of these instruments are glucose meters manufactured by Boeringer Mannheim, Miles, Lifescan, Medisense, Home Diagnostics, and Kyoto Daiichi. However, these meters are intended for continued daily use over months and years, and they are too complex and expensive to be discarded after a single use.